1. Field of the Invention
The invention relates to a heat sensor system, and particularly to an alarm trigger and a heat sensor used as a triggering device in a fire alarm.
Residential and industrial fire detection systems may be broadly categorized as smoke alarms and heat-sensor triggered alarms. The most recent figures available from the U.S. Fire Administration reveal that 6,000 lives were lost in a one-year span, and over $8 billion of direct financial losses were sustained in the U.S. due to fires. While no national standard has been reached, a voluntary standard suggests heat sensors throughout the house and a smoke detector centrally disposed. There are mandatory as well as voluntary requirements. Costs for such a systems range from $10 for a single smoke alarm to well over $1,000 for a system with several smoke alarms and heat sensors.
The correct placement and use of fire alarms is considered by fire fighting authorities as one of the principal methods of fire control. Approximately 85% of homes, and virtually all commercial and industrial buildings in the U.S. are equipped with fire alarms of one type or another. The objective of the fire alarm is to emit a signal which alerts occupants to seek exits, activates fire suppression systems or otherwise notifies fire control personnel.
2. Description of the Related Art
There are several systems for classifying the stages of fire. One of the classification systems includes the following stages:
HEATING PA1 DECOMPOSITION PA1 IGNITION PA1 COMBUSTION AND PYROLYSIS PA1 PROPAGATION (FLAME SPREAD) PA1 PENETRATION PA1 "FLASHOVER" (FULGURATION) PA1 INCINERATION PA1 first electrode means having a first electrode potential; PA1 second electrode means having a second electrode potential different from the first electrode potential; PA1 means for electrically connecting the first and second electrode means to an alarm circuit; PA1 the first and second electrode means defining a space therebetween; PA1 electrolytic material disposed in the space between the first and second electrode means; PA1 the electrolytic material being adjusted such that a current flows between the first and second electrode means sufficient to trigger the alarm circuit at a given temperature. PA1 first and second electrode means having an electrode potential difference and defining a space therebetween; PA1 a switching circuit connected between the first and second electrode means, respectively, and the alarm circuit for triggering the alarm circuit; PA1 electrolyte material disposed in the space between the first and second electrode means, the electrolyte material being adjusted such that a current flows between the first and second electrodes when a given trigger temperature is reached sufficient to switch the switching circuit and to trigger the alarm system.
Most prior art fire detection systems do not respond to the first three stages, and are activated only starting with the fourth stage (combustion and pyrolysis). Infrared detectors could pick up initial heating, if set for automatic detection. Such systems, however, are not widely used as they are expensive, difficult to install, operate and maintain, and they require proper strategic placement.
Several types of detectors are commonly in use: thermal sensors (thermostats, thermopiles and infrared sensors); smoke detectors (photo-electric and ionization detectors); and flame detectors; and product of combustion (gas) detectors. Each type has major drawbacks. Most depend on "line-of-sight" or proximity, for their efficiency, and are frequently blocked from "direct view" of the source locus of the fire.
In many fire alarm systems the sensor component of the system is attached directly to the alarm circuit. The fire signal is picked up from a distance, after a trajectory through intervening space. The sensitivity and thus the effectiveness of the alarm is thus strongly affected.
Since the objective of the alarm component is to alert inhabitants to impending danger, there are numerous types of system outputs to serve this function: sirens, bells, horns, buzzers, loudspeakers, flashing lights, telecommunication signals, etc.
Heat sensors, on the other hand, are based on fire detection by fusible links or other mechanical devices, such as bi-metal trigger probes. The response speed and sensitivity of these devices are essential engineering problems. Since heat sensors must be disposed at least one per room in order to be effective, the cost of installation therefor is quite substantial. In many instances, these devices must be replaced once they have been triggered, adding to the cost of maintenance.
One of the most popular smoke alarm devices is available under the trademark FIRST ALERT, as sold by PITTWAY Corp. Pitway says smoke detectors in general should not be placed in areas with a relatively high density of combustion particles, such as in kitchens, garages, near furnaces, hot water heaters and space heaters. Furthermore, such devices may be triggered by dust, which prevents their use in many industrial environments. Numerous other "forbidden" areas are listed for ionization or smoke detectors, such as in damp or very humid areas, very cold or very hot rooms, bathrooms, dirty areas, near air vents, insect-infested areas and near fluorescent lights.
Maybe the most disadvantageous feature of conventional smoke and fire alarms is the fact that they are operated by batteries, usually alkaline batteries. These are often drained and become inoperative after a certain amount of time because their shelf-life is relatively short.
Some prior art devices are provided with circuits which give off an alarm signal when then battery reaches a dangerously low charge level. The user is thus notified that the battery must be exchanged. Often, of course, the battery is then removed from the device, but it is not exchanged. Other, older, smoke and fire alarms are not provided with these low-charge detectors. The inoperativeness of the battery is thus only detected, when the device is tested.